Modern and future mobile communication systems are designed to provide high-speed, high link-quality, or high security transmissions. They may also support various communication needs, services, or protocols. An effective resource schedule or allocation method may be needed to meet various quality of service (QoS) requirements for different users at different locations. For example, users located at cell boundaries or boundaries of wireless transmissions may have reduced link quality, and users in a cell with a severe shadowing effect may also have a reduced link quality. Without an effective resource schedule or allocation, the reduced link quality may prevent users from having high data-rate transmissions.
One way to resolve the problem is to increase the density of base stations or to place more base stations at areas with severe shadowing or less desirable link quality. This approach may increase costs or require additional equipment or hardware. As an alternative, the transmission power of a base station may be increased to improve link quality, but the approach may increase transmission costs, signal interference, or both.
As another alternative, a multi-hop relay cell architecture may be implemented, which may solve some of the problems in some applications when considering factors such as QoS, deployment costs, transmission power, and coverage areas of cells. Relay stations may be deployed within a cell to relay information from a base station to users or mobile stations. In some applications, the use of relay stations may improve cell coverage, user throughput, system capacity, or any combination of them compared to other alternatives. For example, relay stations may be deployed at areas with severe shadowing, areas near cell boundaries, areas not very well served by base stations, or areas with less desirable link quality. The relay stations therefore may better serve those areas by providing improved link quality and extend the effective coverage of the base stations.
A single link with less desirable quality may be divided into a plurality of links with better quality to enable each link to provide higher transmission rates. However, because the same data may be duplicated and relayed over the air multiple times for multi-hop transmissions, it needs extra radio resources for the extra hop(s) of data transmission. Without a proper scheduling mechanism, it may consume more radio resources than a single-hop system.
In a multi-hop communication system, there may be a base station and several relay stations in a cell. To efficiently utilize the radio resource and to improve the spectrum efficiency, multiple serving stations may be active simultaneously if the interference level is acceptable. For example, the interference may include (1) the potential interference between serving stations (base station and/or relay stations) transmitting at the same time within the same cell is acceptable, (2) the interference from these transmitting serving stations to other cells, or both (1) and (2).
To obtain benefits for multi-hop relay communication systems, there may be a need for a scheduling mechanism for the transmissions of base stations and relay stations. As an example for improving the performance of a wireless communication system, a method of relay stations deployment in a Manhattan-like environment was provided in the Wireless World Initiative New Radio (WINNER) program. The Manhattan-like environment is a grid environment in which the width of blocks is about 200 meters (m) and the width of streets is about 30 m. FIG. 1 is a diagram illustrating a layout of a base station 205 and a plurality of relay stations 201 to 204 in a single cell under a Manhattan-like environment. Referring to FIG. 1, base station 205 and relay stations 201 to 204 may be placed within the single cell. Base station 205 and relay stations 201 to 204 may communicate with users through omni-directional antennas. However, because relay stations 201 to 204 may be outside coverage area 206 of base station 205, each of relay stations 201 to 204 may require an additional directional antenna pointing at base station 205 for communicating with base station 205. This requirement may increase the hardware cost of relay stations.
FIG. 2 is a diagram illustrating the transmission scheduling of a frame structure applicable to the first layout shown in FIG. 1 within a single cell. Referring to FIG. 2, frame S301 may be divided into two sub-frames S302 and S303. The first sub-frame 5302 may be further divided into 5 time slots S304 to S308. Base station 305 may serve four relay stations 301 to 304 during the first four time slots S304 to S307, respectively. During the fifth time slot S308, base station 305 may serve users within area 306, which may directly communicate with base station 305. The second sub-frame S303 may be divided into two time slots S309 and S310, and with the characteristics of spatial separation of the environment, relay stations 301 and 302 may respectively serve their corresponding users within two areas 307 and 308 during the first time slot S309, and relay stations 303 and 304 may respectively serve their corresponding users within areas 309 and 310 during the second time slot S310.
FIG. 3 is a diagram illustrating a layout of base stations 405, 415 and relay stations 401 to 404, 411 to 414 in a multi-cell structure in the Manhattan-like environment illustrated in FIG. 2. Referring to FIG. 3, coverage area 406 of single cell A and coverage area 416 of single cell B are arranged in a staggered manner. Moreover, base stations 405 and 415 in FIG. 4 represent the locations of the base stations in single cell A and single cell B. Relay stations 401 to 404 belong to single cell A, and relay stations 411 to 414 belong to single cell B.
FIG. 4 is a diagram illustrating transmission scheduling for a frame structure applicable to the layout shown in FIG. 3 within the multi-cell structure in the Manhattan-like environment. Referring to FIG. 4, an arrangement of transmission frames between adjacent cells may be used to vary or adjust the operation orders of sub-frames S502 and S503 in frame S501 so that the interference between cells may be reduced. These relay stations may extend the coverage area of the base station. However, the link quality of users at the service range boundary of the base station may have no or limited improvement. Moreover, all of the base stations may have idle time within the periods of frame transmissions. Because base stations may be the only serving stations connected to the backhaul networks and transmitting effective data, the transmission efficiency of the base stations in this design may less desirable.
FIG. 5 is a diagram illustrating a second layout of base station 605 and four relay stations 601 to 604 with omni-directional antennas in a Manhattan-like environment. Referring to FIG. 5, base station 605 and relay stations 601 to 604 may all communicate with users by using omni-directional antennas. Because relay stations 601 to 604 are placed within coverage area 606 of base station 605, additional directional antenna might not be needed by each of relay station 601 to 604 for communicating with base station 605. With this design, the link quality of users in the cell boundary may be improved.
FIG. 6 is a diagram illustrating transmission scheduling for a frame structure applicable to the second layout shown in FIG. 5 with all serving stations equipped with omni-directional antennas in the Manhattan-like environment. Referring to FIG. 6, base station 705 may serve four relay stations 701 to 704 sequentially during first four time slots S701 to S704, and at the same time, base station 705 may serve users directly connected to base station 705. Relay stations 701 and 703 may respectively serve their corresponding users during the time slot S705. After that, relay stations 702 and 704 may respectively serve their corresponding users during the next time slot S706. This layout may improve the link quality of users at the cell boundary. However, a complete transmission within a single cell may require at least 6 phases. When considering the multi-cell structure, because of the use of omni-directional antennas, the reuse factor of at least 2 may be required to avoid severe inter-cell interference, thereby decreasing the overall system capacity.
Under the different layout of base and relay stations, all the base stations and the relay stations may still idle for some time in the frame structure. Accordingly, the transmission efficiency may be undesirable. Therefore, there may be a need for systems or methods for multi-hop relay in wireless communications systems that may provide alternative implementations or applications. The disclosed embodiments may overcome or be configured to overcome one or more of the problems set forth above.